1. Field of the Invention
The present invention relates to a membrane structure and, more particularly, to a membrane structure used for an airship or a membrane structure built on the ground.
2. Description of the Related Art
Conventionally, a non-rigid airship that adopts a gasbag made of a membrane material, instead of an outer shell formed from a hard material such as a light metal, is made lightweight by increasing the strength of the membrane material. However, if an airship flies at a high altitude, where the pressure on the membrane material is significant, a large tensile force is generated on the gasbag. Since the membrane material must have a strength that resists such a large tensile force, it is difficult to reduce the weight of the gasbag. Hence, it is not easy to reduce the weight of the membrane structure.
As membrane structures built on the ground, structures whose shape is maintained by pressurizing the membrane structure from the inside are known. Such membrane structures are often used for simple buildings constructed in exhibition grounds or amusement parks. The structures are also used for the roofs of large buildings such as all-weather baseball and football stadiums. In such structures, a large tensile force is generated in the membrane that must maintain a certain shape against the weight of the membrane itself and forces such as wind pressure. A membrane structure built on the ground therefore must have a membrane resilient to splitting.
Additionally, flying objects that place observation devices or communication devices at predetermined positions for scientific observation or communication in the stratosphere at an altitude of, e.g., 20 to 40 km have been studied. A super-pressure balloon is known as a membrane structure for such purposes. A super-pressure balloon has a gasbag resistant to internal pressure. Even when the balloon reaches the maximum volume, no gas generating buoyancy for rising is discharged. The balloon continuously rises while maintaining the same internal gas pressure. As the air density decreases, the buoyancy decreases. Then, the balloon flies horizontally at a predetermined altitude.
Since a super-pressure balloon has a flat spherical shape, the air resistance is high. Hence, a super-pressure balloon cannot remain at a predetermined position, due to air currents.